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STENCIL-BLANK.

11o JDrawing.

To all whom it may concern:

Be it known that T, CHARLES E. Swmr, a citizen of the United States, residing at Brookline, in the county of Norfolk and State of Massachusetts, have invented certain new and useful Improvements in Sten oil-Blanks, of which the following is a specification.

The present invention relates prlmarily to the manufacture of stencil blanks. For many years stencil blanks have been made from .thin, long fibered tissue paper im pregnated with an ink-resisting material. When a stencil is made from a blank so prepared, a blow by the type of a stencll cutting machine, for example a typewriting machine, ruptures the film of impregnating inleresisting material while leaving the fibers mostly unruptured to serve as bridges to support parts of letters like the center of the letter O or the mclosed parts of letters, for example, the capital letter B.

One of the earlier stencil blanks employed a filling material of wax, usually in practice what is known in commerce as paraffin wax. This is capable of making a useful stencil, but because of the brittleness of wax at relatively low temperatures accidental rupture, due to careless handling, may take place and such rupture permit the ink to penetrate, which is of course undesirable. An- 7 other objection to the wax impregnated stencil blank is that its life when made in til a stencil permits a relatively smaller number of copies to be secured than when other impregnating materlal is used.

' by the use of soluble chromium compounds or by alum or preferably by formaldehyde.

To apply a water solution to tissue paper is not easy mechanically. The paper when wet with water will not support its own weight except in small pieces. If larger piecesof paper are used, they must have some kind of mechanical support when wet.

When it is desired to make a stencil from a blank prepared from coagulated protein, it must be dampened with water before the operation ofcutting. If much time is oc specification of Letters Patent.

Patented fiept. llfi, 1919.

' Application filed March 15,1919. fierial'lto. QWMHM.

cupied in cutting or in very dry weather,

theuncut part of the sheet may have to be taken from the machine for the purpose of again dampening the uncut portion. The subsequent realinement in the machine is inherently troublesome.

It is the main object of the present invention to produce a stencil blank which, having a continuous and homogeneous film, will stand considerable wear without liability to crack or receive other injury at all ordinary temperatures, which is not liable to deterioration from age and need not be dampened before the operation of cutting the stencil.

l[ have discovered that an improved stencil blank may be made from-thin, long fibered tissue paper if instead of impregnating with wax on the one hand or with protein and hygroscopic material on the other, I employ a composition for filling, which is either wholly or in large part composed of aluminum soap of fatty acids. The aluminum soaps of some fatty acids (for instance oleic and palmitic acid) are insoluble in water and possess a rubber like quality. They will dissolve in mineral oil and their likeness to unvulcanized rubber is still more marked in such solution.

In practice preferably use higher fatty acids than oleic, for instance palmitic acid. T have made good stencil blanks by dissolving the aluminum soap made from palm oil in gasolene, impregnating the paper with the solution and then permitting the gasolene to evaporate. The quality of the blanks maybe improved by adding to the gasolene solution of the aluminum soap, some mineral oil nonvolatile at ordinary temperatures. While there is of course some latitude in the selection of the proportions of the aluminum soap and the heavy mineral oil, have found that the mixture of five parts of the aluminum soap and about one part of the heavy mineral oil gives excellent results. Gasolene is used only as a 'solvent. When it evaporates from the solution after application, the aluminum soap and mineral oil are in solid solution and the compound makes an excellent continuous and homogeneous ink-proof film, cuts in distinct lines and the stencil cut is nonhealing.

By applyin solutions containing no water, many of t e usual manufacturing dim culties are avoided. The aluminum soap film material is water-proof and thestencil blank does not require moistening before cutting.

I suggest the following steps for making the solution:

First, I make a neutral water-soluble soap from the desired fatty materials. This is precipitated from a water solution of an gluminum salt, conveniently aluminum sulate.

Second. The aluminum soap is washed and dried, preferably in the dark and at a temperature insufiicient to melt the alumi num soap.

Third. The dry aluminum soap (approximately dry) is covered with gasolene and allowed to swell. It is then warmed and stirred. At this stage, or at any previous one, the mineral oil may be added.

It is understood that this is not the only way of making the compound or solution, but for practical purposes it is probably the best.

I claim: 1. A stencil blank made from long fibered tissue paper impregnated with an aluminum soap of fatty acids comprising the greater part of the filling material.

2. A stencil blank made from long fibered tlssue paper impregnated with a compound containing aluminum soap of fatty acids and a fluid hydrocarbon of the parafiin series, the former comprising the greater part of the filling material.

f3. A stencil blank made from long fibered tissue paper impregnated with an aluminum soap of fatty acids derived principally from palmitic acid, said soap comprising the greater art of the filling material.

4. A stencil blank made from long fibercd tissue paper impregnated with a compound containing aluminum soap of fatty acids and a fluid hydrocarbon of the parafiin series, the former being derived principally from palmitic acid and comprising the greater part of the filling material.

5. A stencil blank made from long fibered tissue paper impregnated with a compound containing the aluminum soap of palmitic acid and mineral oil, the former comprisin over one half the mixture.

In testimony whereof, I allix my signature.

CHARLES E. SWETT. 

